The blunt-headed salamander is a metamorphosing species of mole salamander, which means that it can make the full transition from aquatic larval form to a terrestrial adult form in its lifetime. The adult spends the majority of its time on land in a mosaic of natural grasslands and pine-oak forests. It is highly evolutionarily distinct, the family diverging from all other salamanders in the Early Cretaceous period over 140 million years ago, around five million years before the koala and dolphin lineages diverged from their common ancestor. Today, the desiccation, pollution and conversion of former ponds, small reservoirs, and open habitat to row crops, represents the main threat to the species’ survival.

Urgent Conservation Actions

Clearly protected habitat areas, sensitive land use techniques; the control of introduced predatory fish.

The family Ambystomatidae is also referred to as the mole salamanders because many live in burrows for much for their lives. They are found only in North America (from Canada down to Mexico), the majority (like the blunt-headed salamander) metamorphose from aquatic larvae to become terrestrial adults that are rarely seen except in the breeding season, when they migrate to ponds to mate and deposit eggs.

Evolutionary Distinctiveness

Order: Caudata

Family: Ambystomatidae

The family Ambystomatidae or “the mole salamanders” is included within the four earliest or most primitive family lineages of the order “Caudata” (the salamanders), diverging from all other salamanders in the Early Cretaceous period over 140 million years ago, around five million years before the koala and dolphin lineages diverged from their common ancestor. The small number of species that represent the genus Ambystoma are highly evolutionarily distinct members of both the salamanders and the amphibians as a whole.

The blunt-headed salamander is capable of reaching sexual maturity in its neotenous form, retaining its aquatic larval characteristics such as fins and gills throughout its life. However, it is also able to metamorphose into the adult form and live a terrestrial life. Although this species has been little-studied, there are a couple of theories that may explain why some populations of the blunt-headed salamander do not metamorphose. One idea is that the production or effectiveness of the hormone thyroxine is compromised, either by the species living in water bodies containing insufficient iodine (which is required in the manufacture of thyroxine by the body) or in water temperatures that are too cold for the thyroxine to be effective. This impacts upon the development of the species and sexually mature adults never develop adult characteristics but remain in the larval form. A second theory suggests that species evolving in pools surrounded by hostile terrestrial environments develop aquatic lives to obviate the need to exit the relative safety of their watery home. This is a common trait in species that inhabit high-elevation ponds. Since the blunt-headed salamander inhabits various ponds across its range, and is able to disperse between them in its metamorphosed form, it is possible that the conditions in some of these ponds are not conducive to metamorphosis.

Description

The blunt-headed salamander is an Ambystomatid or mole salamander from high elevations (2,000m above sea level) 15 miles west of Morelia in Michoacán, Mexico. Mole salamanders are medium to large, stocky salamanders, measuring between 90 to 350mm from the tip of the nose to the end of the tail, which salamanders retain throughout their life. Males are often larger than females, partly due to their longer tails. Ambystomatids generally exhibit both aquatic “neotenic” larval (or aquatic and permanently juvenile in form with external, feathery gills) and terrestrial “metamorphosed” (or ground-dwelling, fully developed adult in form with reduced gills) stages in their wild populations. Ambystomatids are often boldly patterned as adults, with well-developed “costal” grooves (successive vertical grooves along the sides of the body), especially the metamorphosing varieties. They have a rather flattened body with a wide, flattened head, a large mouth and smooth skin with many glands. The tail is roundish or laterally compressed, and, during the breeding season, males display a very swollen cloacal zone (the region around the reproductory and excretory opening in amphibians located underneath the base of the tail).

The blunt-headed salamander has both neotenic and fully developed terrestrial (or ground-dwelling) populations. Neotenic populations retain their gills and fins throughout their life, whereas metamorphosed individuals develop adult traits, such as the lack of gills, functioning lungs, eyelids and no fins. These so-called “neotene” individuals are very long with extremely short, blunt heads and round eyes. They are about 150-160 mm in length, with a tail length of around 60-70 mm. The neotenous adults have a dorsal fin along the tail and relatively short, thick gills, although metamorphosed adults lack both fins and gills. The digits are semi-webbed. The colouring of this species is blackish-brown on the dorsal (or upper) surfaces, with a lighter grey under-belly. The end of the tail is darker than the base. The chest and throat have some cream markings. They also display small, dark marks on their head and back.

Ecology

The blunt-headed salamander is a metamorphosing species of mole salamander, which means that it can make the full transition from aquatic larval form to a terrestrial adult form in its lifetime in the wild. The adult blunt-headed salamander spends the majority of its time on land in a mosaic of natural grasslands and pine-oak forests.

Once the eggs are laid in water they are left to develop with no further participation by either parent. This species does not exhibit parental care.

Habitat

The blunt-headed salamander inhabits a mosaic landscape of natural grasslands and pine-oak forest, occurring at about 2,000m above sea level in its small range area around Tacicuaro, north-western Michoacan, to the west of the Morelia City in Mexico. Blunt-headed salamanders require ponds of moderate depth in which to breed, and are able to survive in some types of modified landscape, taking advantage of cattle ponds for larval development.

Distribution

Found in the neotropics in a small area around Tacicuaro, north-western Michoacan, to the west of Morelia City in Mexico. It occurs at about 2,000m above sea level.

There is very little information on the species' population status; there has been limited fieldwork carried out on this species since the early 1980s.

Population Trend

The IUCN Red List of Threatened Species indicates that the blunt-headed salamander’s total population size is generally in decline.

Status

Listed as Critically Endangered on the IUCN Red List of Threatened Species because its extent of occurrence is less than 100km sq. and its area of occupancy is less than 10km sq., its distribution is severely fragmented, and there is continuing decline in the number of mature individuals and in the extent and quality of its habitat around the city of Morelia.

Threats

The desiccation, pollution, and conversion of former ponds, small reservoirs, and open habitat to row crops, represents the main threat to the blunt-headed salamander, coupled with urban expansion of Morelia and Uruapan. Introduced predatory fish are also a major concern, both in ponds and small streams as these may prey extensively on the declining populations of blunt-headed salamanders.

Conservation Underway

The blunt-headed salamander does not occur in any protected areas, although it is protected under the category Pr (Special Protection) by the Government of Mexico.

Conservation Proposed

Conservation and restoration of the natural habitats for the blunt-headed salamander is urgent, and new field surveys are required to assess the status of this species in the wild.
The IUCN Technical Guidelines for the Management of Ex situ Populations, part of the IUCN Red List of Threatened Species, recommend that all Critically Endangered species should have an ex situ population managed to guard against the extinction of the species. An ex situ population is ideally a breeding colony of a species maintained outside its natural habitat, giving rise to individuals from that species that are sheltered from problems associated with their situation in the wild. This can be located within the species’ range or in a foreign country that has the facilities to support a captive breeding programme for that species. It might be possible to breed the blunt-headed salamander in captivity and reintroduce them into the wild, in which case captive animals could be a source of new individuals to repopulate natural habitats whilst its ecosystem is restored and an environmental management plan is developed for this species and its habitat. Further investigation is therefore required into the possibilities of establishing a captive breeding programme for the blunt-headed salamander.

However, any ex situ conservation measure is rendered ineffective if there remains insufficient natural habitat in which to release captive bred populations in the future. Clearly protected areas, sensitive land use techniques and the control of introduced predatory fish populations are urgently required to save this critically endangered mole salamander from extinction in the wild.

Taylor, E. H. 1940. New Salamanders from Mexico, with a discussion of certain known forms. The University of Kansas Science Bulletin 26(12 ): pages 407-439 with 4 plates.

Webb, R.G. 2004. Observations on tiger salamanders (Ambystoma tigrinum complex, Family Ambystomatidae) in Mexico with description of a new species. Bulletin of the Maryland Herpetological Society 40: 122-143.

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